Thanks for the information.
Regarding “a cabling issue”, it can actually be many things. On a fundamental level, if a cable is too long, or the cable is bad quality, it will cause distortion to the signal. The simplest form of distortion is linear voltage drop. For example. putting a 2V peak-to-peak signal into a 100 meter cable, you might get 1V peak-to-peak signal at the other end (just an example, it really depends on the quality of the cable).
At the most fundamental level, signal integrity refers to whether a receiver can adequately differentiate between a logic 0 and logic 1 voltage level (I’m assuming 2 voltage levels, many communication protocols have more than that, but let’s keep this simple).
There are other forms of distortion, such as voltage reflections, increase of rise/fall time, both of which are frequency dependent. I won’t go too much into the physics of it, but generally, using long cable, or using a short, poor quality cable, will affect the integrity of the signal negatively. You can also have problems due to nearby devices generating EMI, which will induce noise in the cable, further reducing signal integrity.
When signal integrity is too poor for gigabit ethernet (1000BASE-T), the switch will automatically downgrade to a slower speed (100BASE-T); slower signals are less susceptible to signal integrity issues.
Anyway, when I say “it’s a cabling issue” it could be one of many factors. In your case, it seems the issue is related to length, so a 10 meter cable isn’t working, and it seems your device is a gigabit device, since it works at 3 and 10 meters.
The specification for standard transformer based ethernet states 100 meters can be achieved using CAT6 cabling for 1000BASE-T (gigabit ethernet). Using transformerless ethernet reduces that maximum distance quite a lot.
The question then becomes “what is the maximum distance I can achieve with transformerless ethernet”. This is really a “how long is a piece of string” question. It depends on the cable type you use, it depends whether there are noisy devices nearby, and it depends on whether the two connected devices share a ground or not.
Intuitively, I wouldn’t suggest using transformerless ethernet for connections exceeding 1 meter or so. Many of our customers have very short connections to make, within a system which shares a single ground; in such situations, transformerless allows us to save space.
So, it may well be that you’re just hitting the limits of the technology by trying to get transformerless ethernet working at 10 meters at 1000BASE-T. That being said, let me know what type of cable you are using (is it a CAT5/6/7 cable? Is it shielded), and let me know if you are using anything else in the signal chain (any adapters), and I can give a better idea of whether it should work. Also let me know if there are noisy EMI sources nearby, and let me know if the connected device shares the same ground as GigaBlox Nano.